This invention relates to lamps and, in particular, to automotive incandescent and other such lamps used in lighting assemblies where the lamp operation can raise the temperature of its plastic components sufficiently high to cause outgassing of those components.
Outgassing of plastics used in exterior vehicle lighting applications is known to cause fogging of the lenses which can adversely affect the appearance and aesthetics of the lens. See, for example, U.S. Pat. No. 6,012,830 to Frazier which discloses a light shield for a vehicle headlamp that uses a titanium carbide coating that reportedly does not outgas over the life of the headlamp. Outgassing has been traced to the release of volatiles from the resin as a result of the polymerization process of some resins. This is particularly true where exterior vehicle incandescent lamps are used in conjunction with a plastic components, since the heat output of the lamps can raise the temperature of the components to 200xc2x0 F.-450xc2x0 F.
One component most directly affected by heat from an automotive incandescent lamp is the plastic sleeve used on certain press-seal (wedge-base) lamps to retain the lead wires in place on the lamp and to provide a mating interface between the lamp and a separate socket. Such lamps are well known in the art. See, for example, U.S. Pat. Nos. 5,186,669 to M. R. Holman et al.; 5,486,991 to G. E. Talmon-Gros et al.; and 5,486,991 to J. D. Bodem et al. These sleeves have traditionally been made from plastic and are designed to slide onto the press-seal base of the lamp and past a set of protrusions on the bulb which thereafter operate to retain the sleeve in place by an interference fit of the sleeve on the bulb""s press-seal base. For this purpose, plastics such as 40% mineral-filled nylon have been used which have sufficient resiliency to permit the sleeve to deform as it passes over the protrusions.
In accordance with one aspect of the present invention, there is provided a lamp having a glass envelope with a polyetherimide sleeve attached to a sealed end of the glass envelope. The glass envelope includes an interior space and a filament or other light emitting element contained within the interior space. The light emitting element is at least partially supported by a plurality of lead wires that extend from the interior space through the glass envelope to an exposed location at the sealed end. The sleeve includes a base portion having an interior passage, with the sleeve being located on the sealed end such that the sealed end extends through the interior passage. The polyetherimide sleeve is capable of withstanding relative high temperature operation without outgassing of the plastic.
In accordance with another aspect of the invention, the lamp is designed such that the sleeve, whether formed from polyetherimide or some other material, includes a locking member in contact with the sealed end. The sealed end includes a bearing surface and the locking member engages the bearing surface such that the sleeve is inhibited from moving away from the interior space and becoming separated from the sealed end. The locking member has a first end attached to the base portion with the locking member extending along the interior passage from the first end to a second, free end that is in engagement with the bearing surface. The first end of the locking member is flexibly attached to the base portion such that the free end can be flexed outwardly away from the interior passage while providing an inwardly directed force. This permits the sleeve to be assembled onto the sealed end and slid towards the interior space with the free end being flexed outwardly during movement of the sleeve towards the interior space and the free end thereafter moving inwardly towards the passage when the free end reaches and engages the bearing surface.